Prep mashed potatoes: Peel and dice 2 medium russet potatoes. Bring a pot of water to a boil, add potatoes, and boil until fork-tender, about 12-15 minutes. Drain and mash with a fork. Stir in 1 cup half and half, ¼ teaspoon garlic salt, and ¼ teaspoon onion salt. Mix until smooth and set aside.
Cook vegetables: In a large skillet, melt 1 tablespoon butter over medium-high heat. Add 1 cup chopped onions and 1 cups diced carrots. Sauté until softened, about 8-10 minutes.
Add garlic: Add 3 cloves minced garlic and cook for 1 minute, stirring frequently.
Cook turkey: Spray the pan lightly with olive oil, then add 1 pound ground turkey breast. Break up the meats with a spatula and cook until no longer pink, about 10 minutes.
Season meat mixture: Stir in ½ teaspoon onion salt, ½ teaspoon garlic salt, ¼ teaspoon dried oregano, and ¼ teaspoon dried thyme. Cook for an additional 2-3 minutes to combine the flavors.
Add tomato paste and Worcestershire sauce: Stir in 1 tablespoon tomato paste and 1 tablespoon Worcestershire sauce. Mix well.
Thicken with flour and broth: Sprinkle 1 tablespoon flour over the meat mixture and stir it in. Pour in 1 cup chicken broth. Simmer for about 5 minutes, until the liquid is mostly absorbed.
Add peas: Stir in ¾ cup frozen peas and remove the pan from heat.
Assemble the pie: Preheat your oven to 400°F (200°C). Grease a 9x13-inch baking dish and spread the turkey filling evenly in the dish. Top with the mashed potatoes, spreading them out smoothly with a fork.
Bake the pie: Place the assembled Shepherd’s Pie in the preheated oven. Bake at 400°F for 25 minutes, or until the top is golden and the filling is bubbly.
Serve: Remove from the oven, allow it to cool slightly, then serve your delicious Turkey Shepherd's Pie!